Applications of ceramics in dentistry are steadily expanding due to outstanding progress in the development and control of materials microstructures, chemistry and processing techniques. Meanwhile, the use of ceramic parts in orthopedic joint replacement procedures remains widespread. Ceramic surfaces are attractive for joint replacement because of low wear rates but they are inherently brittle. As a consequence, even if success rates are generally high, in vivo failures do occur, both in orthopedics and in dentistry. There is a need for reliable, high strength bioceramics with low abrasiveness for use in both orthopedics and dentistry. Our goal is to develop ultrafine-grained zirconia/spinel ceramics with synergistic phase combination leading to high grain boundary stability, high reliability and fracture toughness. This project presents a major technological innovation that relies on 1) the combination of synergistic microstructural and thermal properties between zirconia (3Y-TZP) and ultrafine-grained nanospinel (MgAl2O4) in dual phase bioceramics and 2) the creation of a controlled ultrafine-grained surface inhibiting hydrolytic degradation and reducing abrasiveness. These dual-phase materials will advance the field of bioceramics by ensuring longer life performance in orthopedic and dental applications. In specific Aim 1, zirconia-spinel ceramics (3Y- TZP/nS) will be synthesized and characterized. In specific Aim 2, conditions for grain size refinement will be established and resistance to low temperature degradation (LTD), wear characteristics and mechanical properties of ultrafine-grained 3Y-TZP and 3Y- TZP/nS ceramics will be measured. Expected outcomes of the proposed work are the development and production of novel bioceramics with high strength, high reliability, low abrasiveness while offering excellent esthetics when needed, from the presence of the nanospinel phase. The projected significant reduction in abrasiveness of current zirconia ceramics and novel zirconia-nanospinel bioceramics by developing an innovative grain refinement process constitutes another important translational outcome. The impact of the proposed work will originate from the development of new materials and technology and may extend well beyond orthopedic and dental fields if, as we anticipate, these novel bioceramics exhibit superplasticity, which would greatly facilitate processing at high temperature.